Method for producing bis(fluorosulfonyl)imide salt, method for producing fluorosulfate, and method for producing bis(fluorosulfonyl)imide onium salt

ABSTRACT

According to the method for producing bis(fluorosulfonyl)imide salt of the present invention, the method for producing fluorosulfate, and the method for producing bis(fluorosulfonyl)imide onium salt, first, an aqueous solution is prepared by dissolving a mixed liquid containing bis(fluorosulfonyl)imide and fluorosulfonic acid in water. Then, the aqueous solution is neutralized with an alkaline compound, producing bis(fluorosulfonyl)imide salt and fluorosulfate. In the methods, bis(fluorosulfonyl)imide salt, fluorosulfate, and bis(fluorosulfonyl)imide onium salt can be obtained safely and easily.

TECHNICAL FIELD

The present invention relates to a method for producingbis(fluorosulfonyl)imide salt, a method for producing fluorosulfate, anda method for producing bis(fluorosulfonyl)imide onium salt.

Priority is claimed on Japanese Patent Application No. 2009-084160,filed Mar. 31, 2009, and Japanese Patent Application No. 2009-238344,filed Oct. 15, 2009, the content of which is incorporated herein byreference.

BACKGROUND ART

It has been known that bis(fluorosulfonyl)imide salt ((FSO₂)₂N.M,wherein M is Li, K, NH₄, or the like) is a useful anion source for ionelectrical conducting materials and ion liquids. Also, it has been knownthat fluorosulfate is a useful compound used for ion electricalconducting materials and fire-retardant materials. In addition, it hasbeen known that bis(fluorosulfonyl)imide onium salt is a useful ioniccompound as an ionic liquid.

As a method for producing bis(fluorosulfonyl)imide, the methodsdisclosed in NPL1 and NPL2 have been known. More specifically, in NPL1,a method, in which urea (CO(NH₂)₂) and fluorosulfonic acid (FSO₃H) aremixed first, and then the resulting mixture is heated, allowing thechemical reaction between them to proceed, is disclosed. In thisreaction, the chemical reaction represented by the formula (1) belowproceeds, producing bis(fluorosulfonyl)imide, ammonium hydrogen sulfate(NH₄HSO₄), hydrogen fluoride (HF), and carbon dioxide (CO₂).3FSO₃H+CO(NH₂)₂→(FSO₂)₂NH+NH₄HSO₄+HF+CO₂  (1)

By distilling under reduced pressure during the reaction, a mixed liquidconsisting of the newly produced bis(fluorosulfonyl)imide andfluorosulfonic acid is fractionally distilled. By distilling theobtained mixed liquid further, bis(fluorosulfonyl)imide can berecovered.

In NPL2, a method, in which bis(chlorosulfonyl)imide ((ClSO₂)₂NH) andarsenic trifluoride (AsF₃) are reacted, is disclosed. In this reaction,the chemical reaction represented by the formula (2) below is allowed toproceed, producing bis(fluorosulfonyl)imide and arsenic trichloride(AsCl₃).3(ClSO₂)₂NH+2AsF₃→3(FSO₂)₂NH+2AsCl₃  (2)

After the reaction, the newly produced bis(fluorosulfonyl)amide isdissolved in dichloromethane. The fraction of the newly producedbis(fluorosulfonyl)amide contain fluorosulfonic acid as an impurity. Thecontaminating fluorosulfonic acid can also be dissolved indichloromethane. By adding NaCl to the dichloromethane dissolvingbis(fluorosulfonyl)amide and fluorosulfonic acid, the chemical reactionrepresented by the formula (3) below is allowed to proceed, producingsodium salt of fluorosulfonic acid (FSO₃Na) and hydrogen chloride (HCl).Bis(fluorosulfonyl)imide can be recovered by distilling awaydichloromethane, after removing the precipitated sodium salt offluorosulfonic acid.FSO₃H+NaCl→FSO₃Na+HCl  (3)

As a conventional method for producing bis(fluorosulfonyl)amide salt, amethod, in which bis(fluorosulfonyl)imide is produced by the methodsdisclosed in NPL1 and NPL2, and is neutralized by an alkaline compoundafter dissolving the recovered bis(fluorosulfonyl)imide in water or thelike, has been known, as described in NPL3.

As a conventional method for producing fluorosulfate, a method utilizingthe chemical reaction represented by the formula (3) has been known. Inthe method, the bis(fluorosulfonyl)imide produced by the methodsdisclosed in NPL1 and NPL2. The bis(fluorosulfonyl)amide fractioncontaining fluorosulfonic acid is dissolved in a solvent, such asdichloromethane or the like, and reacted with NaCl, producingfluorosulfate.

As a conventional method for producing bis(fluorosulfonyl)amide oniumsalt, a method, in which bis(fluorosulfonyl)imide is produced by themethods disclosed in NPL1 and NPL2, and an onium compound is added tothe bis(fluorosulfonyl)imide after dissolving thebis(fluorosulfonyl)imide in water or the like, has been known.

RELATED ART DOCUMENT Non-Patent Literature

-   [NPL1] Chem. Bet 95, 246-8 (1962) (Appel&Eisenhauer)-   [NPL2] Inorg. Synth. 11, 138-43 (1968)-   [NPL3] Inorganic Chemistry Vol. 4, 10, 1446-1449 (1965)

DISCLOSURE OF INVENTION Technical Problem

In producing bis(fluorosulfonyl)imide, the methods using urea andfluorosulfonic acid is industrially advantageous, since it takes shortperiod of time for the reaction process and the precursors for thereaction is inexpensive. However, it is known that the fluorosulfonicacid, which is one of the raw materials for the reaction, is anextremely strong acid, and sulfuric acid and hydrogen fluoride areformed when a part of the fluorosulfonic acid is degraded in the methoddisclosed in NPL1 where urea and fluorosulfonic acid are used. As aresult, commonly used apparatuses made of glass or metal are corroded bythe reaction liquid, when the mixed liquid of bis(fluorosulfonyl)amidand fluorosulfonic acid is recovered from the reaction liquid producedfrom the chemical reaction represented by the formula (1), by distillingunder reduced pressure.

In addition, in the method disclosed in NPL1, in whichbis(fluorosulfonyl)imide and fluorosulfonic acid in the mixture areseparated by distillation, the separation of thebis(fluorosulfonyl)imide from the fluorosulfonic acid is difficult,since the boiling point of bis(fluorosulfonyl)imide (170° C.) is closeto that of fluorosulfonic acid (163° C.).

In the method for recovering bis(fluorosulfonyl)imide (that is, a methodfor producing sodium salt of fluorosulfonic acid) disclosed in NPL2, theapparatus for the production is corroded by a large amount of hydrogenchloride gas produced as a by-product. In addition, disposing the sodiumsalt of fluorosulfonic acid separated by straining is difficult, sincehydrogen chloride gas evaporates for several days.

In the conventional method for producing bis(fluorosulfonyl)imide saltdisclosed in NPL3, the bis(fluorosulfonyl)imide salt is contaminated byimpurities such as fluoride ions or the like, since part of thebis(fluorosulfonyl)imide salt undergoes hydrolysis during the process ofdistilling away of water. As a result, it is difficult to recoverbis(fluorosulfonyl)imide salt having a high purity in the methoddisclosed in NPL3.

The present invention was made under circumstances described above. Thepurpose of the present invention is to provide a method for producingbis(fluorosulfonyl)imide salt that enables a highly purebis(fluorosulfonyl)imide salt to be recovered, safely and easily.

Another purpose of the present invention is to provide a method forproducing fluorosulfonic acid safely and easily.

Another purpose of the present invention is to provide a method forproducing bis(fluorosulfonyl)imide onium salt safely and easily.

Solution to Problem

After intensive research, the inventors of the present invention foundthe following. In the presence of bis(fluorosulfonyl)imide,fluorosulfonic acid can be dissolved in water. By neutralizing the waterdissolving the mixed liquid consisting of bis(fluorosulfonyl)imide andfluorosulfate, with an alkaline compound, bis(fluorosulfonyl)imide saltand fluorosulfonic acid can be recovered. Particularly, in case of thebis(fluorosulfonyl)imide salt or the fluorosulfonic acid having a lowsolubility in the neutralized solution, they are precipitated andseparated from the neutralized solution. Thus, the intended salts can beobtained by a separation process using a separation funnel, filtration,or the like.

The first aspect of the present invention is a method for producingbis(fluorosulfonyl)imide salt comprising: a step of dissolving, in whicha mixed liquid containing bis(fluorosulfonyl)imide and fluorosulfonicacid is dissolved in water to prepare an aqueous solution; a step ofneutralizing, in which the aqueous solution is neutralized by an alkalicompound to prepare a neutralized solution; and a step of recoveringbis(fluorosulfonyl)imide salt, in which bis(fluorosulfonyl)imide salt isrecovered from the neutralized solution. In the method,bis(fluorosulfonyl)imide salt may be recovered in the step of recoveringbis(fluorosulfonyl)imide salt by extracting the neutralized solutionwith an organic solvent. Also, in the method, the mixed liquid dissolvedin water in the step of dissolving may be a reaction liquid produced bya reaction between urea and fluorosulfonic acid. Also, in the method,the alkaline compound used in the step of neutralizing may be onecompound selected from the group consisting of MOH, M₂CO₃, MHCO₃,ammonia, and amine, wherein M in the chemical formulae, represents oneselected from the group consisting Na, K, Li, and ammonium cation.

Also, in the method, a content amount of fluorine ion inbis(fluorosulfonyl)imide salt after the step of recovery may be 100 ppmor less. Also, in the method, a content amount of fluorine ion inbis(fluorosulfonyl)imide salt after the step of recovery may be 20 ppmor less.

The second aspect of the present invention is a method for producingfluorosulfate comprising: a step of dissolving, in which a mixed liquidcontaining bis(fluorosulfonyl)imide and fluorosulfonic acid is dissolvedin water to prepare an aqueous solution; a step of neutralizing, inwhich the aqueous solution is neutralized by an alkali compound toprepare a neutralized solution; and a step of recovering fluorosulfate,in which fluorosulfate is recovered from the neutralized solution. Inthe method, fluorosulfate may be recovered in the step of recoveringfluorosulfate by straining fluorosulfate precipitated in the neutralizedsolution. Also, in the method, the mixed liquid dissolved in water inthe step of dissolving may be a reaction liquid produced by a reactionbetween urea and fluorosulfonic acid. Also, in the method, the alkalinecompound used in the step of neutralizing may be one compound selectedfrom a group consisting of MOH, M₂CO₃, MHCO₃, ammonia, and amine,wherein M in the chemical formulae, represents one selected from a groupconsisting of Na, K, Li, and ammonium cation.

The third aspect of the present invention is a method for producingbis(fluorosulfonyl)imide onium salt comprising: a step of dissolving, inwhich a mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid is dissolved in water to prepare an aqueoussolution; a step of neutralizing, in which the aqueous solution isneutralized by an alkali compound to prepare a neutralized solution; anda step of adding an onium compound to the neutralized solution. In themethod, the mixed liquid dissolved in water in the step of dissolvingmay be a reaction liquid produced by a reaction between urea andfluorosulfonic acid. Also, in the method, the alkaline compound used inthe step of neutralizing may be one compound selected from the groupconsisting of MOH, M₂CO₃, MHCO₃, ammonia, and amine, wherein M in thechemical formulae, represents one selected from the group consisting Na,K, Li, and ammonium cation.

Advantageous Effects of Invention

According to the method for producing bis(fluorosulfonyl)imide salt ofthe present invention, first, an aqueous solution is prepared bydissolving a mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid in water. Then, the aqueous solution is neutralizedwith an alkaline compound, producing bis(fluorosulfonyl)imide salt andfluorosulfate. By recovering bis(fluorosulfonyl)imide salt from theneutralized solution, a highly pure bis(fluorosulfonyl)imide salt can beobtained safely and easily.

In the case where the bis(fluorosulfonyl)imide salt is dissolved in theneutralized solution, the bis(fluorosulfonyl)imide salt can be extractedfrom the neutralized solution by an organic solvent. In this way, thebis(fluorosulfonyl)imide salt alone can be selectively separated fromthe neutralized solution.

According to the method for producing fluorosulfate of the presentinvention, first, an aqueous solution is prepared by dissolving a mixedliquid containing bis(fluorosulfonyl)imide and fluorosulfonic acid inwater. Then, the aqueous solution is neutralized with an alkalinecompound, producing bis(fluorosulfonyl)imide salt and fluorosulfate. Byrecovering fluorosulfate from the neutralized solution, a highly purefluorosulfate can be obtained safely and easily.

In the case where the fluorosulfate is precipitated in the neutralizedsolution, the fluorosulfate can be separated by filtering theneutralized solution. In this way, the fluorosulfate alone can beseparated from the neutralized solution selectively.

According to the method for producing bis(fluorosulfonyl)imide oniumsalt of the present invention, first, an aqueous solution is prepared bydissolving a mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid in water. Then, the aqueous solution is neutralizedwith an alkaline compound, producing bis(fluorosulfonyl)imide salt andfluorosulfate. By adding an onium compound to the neutralized solutionand changing salts of the bis(fluorosulfonyl)imide salt in theneutralized solution, the bis(fluorosulfonyl)imide onium salt can beobtained safely and easily.

BEST MODE FOR CARRYING OUT THE INVENTION

The method for producing bis(fluorosulfonyl)imide salt, the method forproducing fluorosulfate, and the method for producingbis(fluorosulfonyl)imide onium salt of the present invention areexplained in detail below.

[Method for Producing bis(fluorosulfonyl)imide salt]

The method for producing bis(fluorosulfonyl)imide salt of the presentinvention includes, a step of dissolving, in which a mixed liquidcontaining bis(fluorosulfonyl)imide and fluorosulfonic acid is dissolvedin water to prepare an aqueous solution (step of preparing an aqueoussolution), a step of neutralizing, in which the aqueous solution isneutralized by an alkali compound to prepare a neutralized solution(step of preparing a neutralized solution), and a step of recoveringbis(fluorosulfonyl)imide salt, in which bis(fluorosulfonyl)imide salt isrecovered from the neutralized solution (step of recovering). Each stepis explained in detail below.

[Step of Preparing an Aqueous Solution]

In the step of preparing an aqueous solution, first, a mixed liquidcontaining bis(fluorosulfonyl)imide and fluorosulfate is obtained. It ispreferable that the mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid is a reaction liquid between urea (CO(NH₂)₂) andfluorosulfonic acid (FSO₃H), even though it is not particularly limitedto this configuration.

For the reaction between urea (CO(NH₂)₂) and fluorosulfonic acid(FSO₃H), the conventional reaction represented in the formula (4)disclosed in NPL1, shown below, can be employed.3FSO₃H+CO(NH₂)₂→(FSO₂)₂NH+NH₄HSO₄+HF+CO₂  (4)

By distilling under reduced pressure during the reaction represented bythe formula (4), a mixed liquid consisting of the newly producedbis(fluorosulfonyl)imide and fluorosulfonic acid, which is a precursorof the reaction, can be fractionally distilled.

The present embodiment is not limited by the method to obtainbis(fluorosulfonyl)imide and fluorosulfonic acid based on the methoddisclosed in NPL1, and they can be obtained by another chemicalreaction.

After obtaining the mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid, the mixed liquid is dissolved in water. Apreferable amount of the water ranges from 1 to 50 parts by masscorresponding to that of the mixed liquid. More preferable amount of thewater ranges from 2 to 10 parts by mass corresponding to that of themixed liquid.

Normally, in the case where fluorosulfonic acid has contacted to water,fluorosulfonic acid reacts extremely vigorously, decomposing it tohydrogen fluoride and sulfuric acid. However, in the method described inthis embodiment of the present invention, contacting fluorosulfonic acidwith water does not cause the extremely vigorous decomposing reaction.It is interpreted that this inertness of fluorosulfonic acid againstwater is due to the presence of ammonia or the like, which is formed bydecomposition of bis(fluorosulfonyl)imide or urea, in the final reactionsolution produced by the reaction between urea and fluorosulfonic acid.The presence of ammonia is believed to extremely reduce the rate ofdecomposition of fluorosulfonic acid in water. As a result, in thisembodiment of the present invention, an aqueous solution dissolving themixed liquid consisting bis(fluorosulfonyl)imide and fluorosulfonicacid, can be prepared in a mild condition.

[Step of Preparing a Neutralized Solution]

Then, the above-mentioned aqueous solution is neutralized by an alkalinesolution quickly, to prepare a neutralized solution. A preferable pH ofthe neutralized solution at the end ranges from 4 to 10. More preferablepH of the neutralized solution at the end ranges from 7 to 9. It is notpreferable for the neutralized solution to have a pH under 4, sinceproduction of fluorosulfate and bis(fluorosulfonyl)imide salt isinsufficient. It is not preferable for the pH to be over 10, since thedecomposition of fluorosulfate and bis(fluorosulfonyl)imide salt isallowed to proceed. By the neutralized solution having a pH in thepreferable ranges, the production of fluorosulfate andbis(fluorosulfonyl)imide salt is sufficient, and the decompositionthereof can be suppressed. Thus they are preferable.

The alkaline solution used for neutralizing the aqueous solution can bean aqueous solution containing an alkaline compound selected from thegroup consisting of MOH, M₂CO₃, MHCO₃, ammonia (NH₃), and amine(NR₁R₂R₃), wherein M in the chemical formulae, represents one selectedfrom the group consisting Na, K, Li, and ammonium cation.

As a more specific example of the alkaline compound, sodium hydroxide(NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), ammoniumhydroxide (R₁R₂R₃R₄NOH), sodium carbonate (Na₂CO₃), potassium carbonate(K₂CO₃), lithium carbonate (Li₂CO₃), sodium bicarbonate (NaHCO₃),potassium bicarbonate (KHCO₃), lithium bicarbonate (LiHCO₃), ammoniumbicarbonate ((R₁R₂R₃R₄N)HCO₃), ammonia (NH₃), or the like can be used.

The ammonium cation (R₄—N⁺R₁R₂R₃) is not particularly limited, and canbe any one of the ammonium ion, the primary ammonium cation, thesecondary ammonium cation, the tertiary ammonium cation, and thequaternary ammonium cation. Each of R₁, R₂, R₃, and R₄ represents ahydrogen atom (H), and an aliphatic or an aromatic alkyl group. In thepresent embodiment of the present invention, a mixture of alkyl groupsselected from the group consisting of methyl-, ethyl-, butyl-, pentyl-,hexyl-, octyl-, decyl-, dodecyl-, tetradecyl-, hexadecyl-, octadecyl-,octadecenyl-, octadecadienyl-, phenyl-groups, or the like can be used.

The amine can be the primary amine, the secondary amine, or the tertiaryamine. Selection of the primary amine is not particularly limited, andit can be ethylamine, n-propylamine, iso-propylamine, n-butylamine,iso-butylamine, sec-butylamine, t-butylamine, ethanolamine,n-propanolamine, iso-propanolamine, 4-amino-1-butanol,2-amino-1-butanol, 1-amino-2-butanol, ethylenediamine,1,3-propanediamine, 1,4-butanediamine, 1,6-hexamethylenediamine, or thelike. Selection of the secondary amine is not particularly limited, andit can be diethylamine, di-n-propylamine, di-iso-propylamine,di-n-butylamine, di-iso-butylamine, di-sec-butylamine, diethanolamine,di-n-propanolamine, di-iso-propanolamine, or the like. Selection of thetertiary amine is not particularly limited, and it can be triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, triethanolamine, tri-n-propanolamine,tri-iso-propanolamine, or the like.

By preparing a neutralized solution by neutralizing the above-mentionedaqueous solution with an alkaline compound, bis(fluorosulfonyl)imidesalt ((FSO₂)₂N.M) and fluorosulfate (FSO₃.M) can be produced.

As bis(fluorosulfonyl)imide salt ((FSO₂)₂N.M), bis(fluorosulfonyl)imidesodium salt, bis(fluorosulfonyl)imide potassium salt,bis(fluorosulfonyl)imide lithium salt, or bis(fluorosulfonyl)imideammonium salt can be produced.

As fluorosulfate (FSO₃.M), sodium fluorosulfate, potassiumfluorosulfate, lithium fluorosulfate, or ammonium fluorosulfate can beproduced.

[Step of Recovering]

Next, bis(fluorosulfonyl)imide salt is recovered from the neutralizedsolution. In the case where the solubility of thebis(fluorosulfonyl)imide salt is low in the neutralized solution, thebis(fluorosulfonyl)imide salt can be recovered from the neutralizedsolution by a separation process, such as separation with a separationfunnel (separating the bis(fluorosulfonyl)imide salt in liquid state),filtration (separating the bis(fluorosulfonyl)imide salt in solidstate), or the like.

In the case where the bis(fluorosulfonyl)imide salt is dissolved in theneutralized solution, the bis(fluorosulfonyl)imide salt can be extractedfrom the neutralized solution by utilizing an organic solvent. In thisextraction with an organic solvent, the bis(fluorosulfonyl)imide saltalone can be selectively separated from the neutralized solution.Selection of the organic solvent used for extracting thebis(fluorosulfonyl)imide salt from the neutralized solution is notparticularly limited as long as it dissolves thebis(fluorosulfonyl)imide salt and forms an organic phase separated fromthe aqueous phase. As the organic solvent forming an organic phaseseparated from the aqueous phase, acetic acid ester solvents arepreferable. In particular, ethyl acetate is more preferable.

A preferable amount of the organic solvent for extracting thebis(fluorosulfonyl)imide salt ranges from 1 to 50 parts by masscorresponding to that of the bis(fluorosulfonyl)imide salt. A morepreferable amount of the organic solvent ranges from 10 to 20 parts bymass corresponding to that of the bis(fluorosulfonyl)imide salt. It isnot preferable to use less than 10 parts by mass of an organic solventto that of the bis(fluorosulfonyl)imide salt, since thebis(fluorosulfonyl)imide salt cannot be extracted sufficiently. Usingmore than 50 parts by mass of the organic solvent to that of thebis(fluorosulfonyl)imide salt is economically wasteful. It is preferablethat the amount of the organic solvent used for the extraction fallsbetween the ranges mentioned above, since the bis(fluorosulfonyl)imidesalt can be sufficiently extracted.

In the case where the produced bis(fluorosulfonyl)imide salt is in thesolid state at room temperature, the bis(fluorosulfonyl)imide salt canbe obtained as a crystal by distilling away the organic solvent or thelike used for the extraction.

The bis(fluorosulfonyl)imide salt can be produced as explained above.

Compounds having a fluoride-containing anion, such asbis(fluorosulfonyl)imide salt are known as useful anion sources for ionelectrical conducting materials, electrolytes, and ion liquids. In thecase where the fraction of the bis(fluorosulfonyl)imide salt containinga large amount of fluoride ions as impurities is used, the contaminatingfluoride ions cause corrosion of an apparatus and deterioration ofplastic. Therefore, it is preferable that the amount of the fluoride ionin the fraction of the bis(fluorosulfonyl)imide is low.

In the conventional method for producing bis(fluorosulfonyl)imide saltas disclosed in NPL3, a part of the bis(fluorosulfonyl)imide saltundergoes hydrolysis in the process where water is distilled away. Thishydrolysis of the bis(fluorosulfonyl)imide salt results in formation ofthe fluoride ions or the like as impurities in the fraction of thebis(fluorosulfonyl)imide salt. Consequently, the recovered fraction ofthe bis(fluorosulfonyl)imide salt is contaminated with a large amount ofimpurities. More specifically, the recovered fraction of thebis(fluorosulfonyl)imide salt has included fluoride ions of severalhundreds ppm to several thousands ppm as impurities. In NPL3, apurification method with recrystallization using ethanol is alsodisclosed. However, there was almost no effect on the reduction of theamount of the fluoride ions by the recrystallization.

On the other hand, in the method for producing bis(fluorosulfonyl)imidesalt of the present invention, bis(fluorosulfonyl)imide salt isprecipitated in an aqueous solution containing bis(fluorosulfonyl)imidesalt. In the case where bis(fluorosulfonyl)imide salt is dissolved in asolution, the bis(fluorosulfonyl)imide salt alone is extractedselectively with an organic solvent, and by distilling away the organicsolvent, the bis(fluorosulfonyl)imide salt is obtained. Accordingly,there is no need to heat treat bis(fluorosulfonyl)imide salt in water.Therefore, the occurrence of hydrolysis of bis(fluorosulfonyl)imide saltby water is extremely low, and the amount of impurities in the fractionof bis(fluorosulfonyl)imide salt can be reduced. Due to reasonsdescribed above, highly pure bis(fluorosulfonyl)imide salt can berecovered.

The amount of fluoride ions contained in the fraction ofbis(fluorosulfonyl)imide salt can be measured for example by theion-chromatography method. The measurement of the content of fluorideions can be performed as described below.

First, a sample for measurement is prepared by dissolving 0.5 g of thespecimen in the 50 mL of ion-exchange water. Then, the measurement ofthe content of fluoride ion in the sample is performed using for examplethe ion-chromatography system ICS-2000 manufactured by DIONEXcorporation (column: IonPacAS19, detector: conductivity detector). Theelution solution is a potassium hydroxide solution in the concentrationof 20 mmol/L (flow rate is 1.0 mL/min).

[Method for Producing Fluorosulfate]

The method for producing fluorosulfate of the present inventionincludes, a step of dissolving, in which a mixed liquid containingbis(fluorosulfonyl)imide and fluorosulfonic acid is dissolved in waterto prepare an aqueous solution (step of preparing an aqueous solution),a step of neutralizing, in which the aqueous solution is neutralized byan alkali compound to prepare a neutralized solution (step of preparinga neutralized solution), and a step of recovering fluorosulfate, inwhich fluorosulfate is recovered from the neutralized solution (step ofrecovering). Since, the step of preparing an aqueous solution and thestep of preparing a neutralized solution are identical to thoseexplained in the method for producing bis(fluorosulfonyl)imide salt,details of the steps are omitted.

[Step of Recovering]

Fluorosulfate is recovered from the neutralized solution prepared in thestep of preparing a neutralized solution. Generally, the solubility offluorosulfate in the neutralized solution is low. Thus, it is often thecase that fluorosulfate is precipitated as a solid from the neutralizedsolution. Therefore, by applying a separation process such as filtrationor the like to the neutralized solution, fluorosulfate can be recoveredfrom the neutralized solution.

In the case where the solubility of the fluorosulfate is high,fluorosulfate and bis(fluorosulfonyl)imide salt can be separated byapplying a separating process appropriately selected from thosedescribed in the step of recovering bis(fluorosulfonyl)imide saltdescribed above.

[Method for Producing bis(fluorosulfonyl)imide onium salt]

The method for producing bis(fluorosulfonyl)imide onium salt of thepresent invention includes, a step of dissolving, in which a mixedliquid containing bis(fluorosulfonyl)imide and fluorosulfonic acid isdissolved in water to prepare an aqueous solution (step of preparing anaqueous solution), a step of neutralizing, in which the aqueous solutionis neutralized by an alkali compound to prepare a neutralized solution(step of preparing a neutralized solution), and a step of adding anonium compound to the neutralized solution (step of adding an oniumcompound). Since the step of preparing an aqueous solution and the stepof preparing a neutralized solution are identical to those explained inthe method for producing bis(fluorosulfonyl)imide salt, details of thesteps are omitted.

[Step of Adding an Onium Compound]

An onium compound is added to the neutralized solution prepared in thestep of preparing the neutralizing solution. By the addition of an oniumcompound, salt substitution occurs between the producedbis(fluorosulfonyl)imide salt ((FSO₂)₂N.M) and the onium compound. As aresult, an ionic compound made of an anion of bis(fluorosulfonyl)imide((FSO₂)₂N⁻) and the onium salt is produced.

Selection of the onium compound is not particularly limited. Saltsincluding onium cations, halogen ions, nitrate ions, sulfate ions,phosphate ions, perchlorate ions, methane sulfate ions, toluene sulfateions, and the like are given as examples.

Selection of the onium cation is not particularly limited, as long as itis a cation having at least one organic group that is formed by acoordination between a compound with a lone electron pair and a cationicatomic group. Nitrogen, sulfur, oxygen, phosphorus, selenium, tin,iodine, and antimony are examples of compounds with a lone electronpair. As onium ions that can be used in the present invention and belongto the symmetric ammonium cation group, tetramethylammonium cations,tetraethylammonium cations, and tetrapropylammonium cations areexamples. As onium ions that can be used in the present invention,belong to the ammonium cation group, and the number of carbon atoms inthe shortest substituent group corresponds to 50% or higher and lessthan 100% of the number of carbon atoms in the longest substituent group(referred as pseudo-symmetric hereinafter), ethyltrimethylammoniumcations, vinyltrimethylammonium cations, triethylmethylammonium cations,triethylpropylammonium cations, diethyldimethylammonium cations,tributylethylammonium cations, triethylisopropylammonium cations, N,N-dimethylpyrrolidinium cations, N-methyl-N-ethylpyrrolidinium cations,triethylmethoxymethylammonium cations, and the like are examples. Asonium ions that can be used in the present invention and belong to theasymmetric ammonium cation group, trimethylpropylammonium cations,trimethylisopropylammonium cations, butyltrimethylammonium cations,allyltrimethylammonium cations, hexyltrimethylammonium cations,octyltrimethylammonium cations, dodecyltrimethylammonium cations,triethylmethoxyethoxymethylammonium cations, dimethyldipropylammoniumcations, and the like are examples. As onium ions that can be used inthe present invention and belong to the divalent ammonium cation group,hexamethonium cations and the like are exemplified. As onium ions thatcan be used in the present invention and belong to the symmetricimidazolium cation group, 1,3-dimethylimidazolium cations,1,3-diethylimidazolium cations, 1,3-dipropylimidazolium cations,1,3-dipropylimidazolium cations, and the like are examples. As oniumions that can be used in the present invention and belong to theasymmetric imidazolium cation group, 1-ethyl-3-methylimidazoliumcations, 1-methyl-3-propylimidazolium cations,1-butyl-3-methylimidazolium cations, 1-isopropyl-3-propylimidazoliumcations, 1-tert-butyl-3-isopropylimidazolium cations, and the like areexamples. As onium ions that can be used in the present invention andbelong to the pyridinium cation group, N-ethylpyridinium cations,N-butylpyridinium cations, and the like are examples. As onium ions thatcan be used in the present invention and belong to the symmetricsulfonium cation group, trimethylsulfonium cations, triethylsulfoniumcations, tributylsulfonium cations, and the like are examples. As oniumions that can be used in the present invention and belong to thepseudo-symmetric sulfonium cation group, eiethilmetilsulfonium cationsand the like are exemplified. As onium ions that can be used in thepresent invention and belong to the asymmetric sulfonium cation group,dimethylpropylsulfonium cations, dimetylhexylsulfonium cations, and thelike are examples. As onium ions that can be used in the presentinvention and belong to the symmetric phosphonium cation group,tetramethylphosphonium cations, tetraethylphosphonium cations,tetrapropylphosphonium cations, tetrabutylphosphonium cations,tetraoctylphosphonium cations, tetraphenylphosphonium cations, and thelike are examples. As onium ions that can be used in the presentinvention and belong to the pseudo-symmetric phosphonium cation group,trimethilethyl phosphonium cations, triethylmethylphosphonium cations,and the like are examples. As onium ions that can be used in the presentinvention and belong to the asymmetric phosphonium cation group,hexyltrimethylphosphonium cations, trimethyloctylphosphonium cations,and the like are examples.

In this embodiment of the present invention, it is preferable to use theonium salts belonging to the imidazole system or the ammonium system.Bis(fluorosulfonyl)imide onium salt can be produced as explained above.

As explained above, according to the method for producingbis(fluorosulfonyl)imide salt of the present invention, first, anaqueous solution is prepared by dissolving a mixed liquid containingbis(fluorosulfonyl)imide and fluorosulfonic acid in water. Then, theaqueous solution is neutralized with an alkaline compound, producingbis(fluorosulfonyl)imide salt and fluorosulfate. By recoveringbis(fluorosulfonyl)imide salt from the neutralized solution, a highlypure bis(fluorosulfonyl)imide salt can be obtained safely and easily.

In the case where the bis(fluorosulfonyl)imide salt is dissolved in theneutralized solution, the bis(fluorosulfonyl)imide salt can be extractedfrom the neutralized solution by an organic solvent. In this way, thebis(fluorosulfonyl)imide salt alone can be selectively separated fromthe neutralized solution.

According to the method for producing fluorosulfate of the presentinvention, first, an aqueous solution is prepared by dissolving a mixedliquid containing bis(fluorosulfonyl)imide and fluorosulfonic acid inwater. Then, the aqueous solution is neutralized with an alkalinecompound, producing bis(fluorosulfonyl)imide salt and fluorosulfate. Byrecovering fluorosulfate from the neutralized solution, a highly purefluorosulfate can be obtained safely and easily.

In the case where the fluorosulfate is precipitated in the neutralizedsolution, the fluorosulfate can be separated by filtering theneutralized solution. In this way, the fluorosulfate alone can beselectively separated from the neutralized solution.

According to the method for producing bis(fluorosulfonyl)imide oniumsalt of the present invention, first, an aqueous solution is prepared bydissolving a mixed liquid containing bis(fluorosulfonyl)imide andfluorosulfonic acid in water. Then, the aqueous solution is neutralizedwith an alkaline compound, producing bis(fluorosulfonyl)imide salt andfluorosulfate. By adding an onium compound to the neutralized solutionand changing salts of the bis(fluorosulfonyl)imide salt in theneutralized solution, the bis(fluorosulfonyl)imide onium salt can beobtained safely and easily.

EXAMPLES

The advantageous effect of the present invention is explained in detailwith Examples below. The present invention is not limited byconfiguration detailed in the Examples.

Example 1

First, 3.2 kg of fluorosulfonic acid was placed in a reaction containerwhose internal volume is 5 L. The reaction container was made ofpolytetrafluoroethylene (PTFE) and equipped with a mixer and athermometer. Then, 800 g of urea was added to the fluorosulfonic acid inthe container little by little with cooling to prepare a fluorosulfonicacid solution containing urea.

In another reaction container whose internal volume was 5 L, 2.4 kg offluorosulfonic acid and 80 g of bis(fluorosulfonyl)imide were placed.The surface of the container is made of stainless and coated with PTFE.The container was equipped with a mixer, a thermometer, and a gasflowmeter. Then, the fluorosulfonic acid solution containing urea wasdripped in the container with a metering pump at the rate of 525 g/Hr,while the content of the container was heated to 120° C.

Once the dripping started, gaseous carbon dioxide was generated. At theendpoint of the dripping, the volume of the gas reached 299 L. The finalreaction solution was cooled down to room temperature. Then, 15 kg ofwater was dripped into the final reaction solution little by little,having the water dissolved in the final reaction solution. Then, 3.6 kgof potassium carbonate was added to the solution to neutralize thesolution and the pH of the solution increased to 9. Then, precipitatedcrystals was obtained by filtering the neutralized solution. By dryingthe crystals at 60° C., 4.4 kg of bis(fluorosulfonyl)imide potassiumsalt was obtained. The solution passing through the filter was extractedwith 7 kg of ethyl acetate twice, and with 2 kg of ethyl acetate once.

Then, the ethyl acetate phase was washed with water, the ethyl acetatewas distilled away, and 1081 g of bis(fluorosulfonyl)imide potassiumsalt was obtained as residue (the recovery based on the precursor ureawas 37%). The content of fluoride ions in the specimen was measured withthe ion-chromatography system ICS-2000 manufactured by DIONEXcorporation (column: IonPacAS19, detector: conductivity detector). Theelution solution was potassium hydroxide solution in the concentrationof 20 mmol/L (flow rate is 1.0 mL/min) Based on the measurement, thecontent of fluoride ion in the sample was 3 ppm. The boiling point ofthe obtained bis(fluorosulfonyl)imide potassium salt was 103 to 104° C.When the samples was analyzed with ¹⁹F-NMR analysis, the peak at 53.5ppm was detected (solvent: DMSO-d, internal standard compound: CFCl₃).

Example 2 Example of Ammonium Salt

The final reaction solution that was cooled down to room temperature wasobtained as in the Example 1. The final reaction solution was dissolvedin 15 kg of water. Then, the solution was neutralized with 2.0 kg of 28%aqueous ammonia, having the pH of the solution increased to 7. Then, theneutralized solution was extracted with 7 kg of ethyl acetate twice andwith 2 kg of ethyl acetate once. The resulting ethyl acetate phase waswashed with water. Then, the ethyl acetate in the extracting phase wasdistilled away. In this way, 792 g of bis(fluorosulfonyl)imide ammoniumsalt was obtained as residue (the recovery based on the precursor ureawas 30%). The content of fluoride ion in the obtainedbis(fluorosulfonyl)imide ammonium salt was 3 ppm. The boiling point ofthe sample was 85 to 88° C.

Example 3 Example Using Li

One hundred grams of the final reaction solution prepared as describedin the Example 1 was dissolved in 200 g of water. Then, the solution wasneutralized with 46 g of lithium carbonate, causing the pH of thesolution to increase to 7. After filtering out the excess lithiumcarbonate, the aqueous phase was extracted with 100 g of ethyl acetatetwice, and with 30 g of ethyl acetate once. The obtained ethyl acetatephase was washed with 30 g of ion exchange water. Then, the ethylacetated in the extracting solution was distilled away. In this way,14.5 g of bis(fluorosulfonyl)imide lithium salt was obtained as residue(the recovery based on the precursor urea was 35%). The content of thefluoride ion in the obtained bis(fluorosulfonyl)imide lithium salt was 8ppm.

Example 4

Two hundred grams of the final reaction solution prepared as describedin the Example 1 was dissolved in 800 g of water. Then, the solution wasneutralized with 52 g of potassium carbonate, having the pH of thesolution increased to 7. The precipitated fluorosulfate potassium saltwas filtered out. Then, an aqueous solution dissolving 37 g oftetrapropylammonium bromide was dripped into the filtered neutralizedsolution. Once the dripping started, crystals ofbis(fluorosulfonyl)imide tetrapropylammonium salt were precipitated out.After recovering the precipitated crystals by filtration, they weredried in a drier set at 60° C. In this way, 48 g ofbis(fluorosulfonyl)imide tetrapropylammonium salt was obtained (therecovery based on the precursor urea was 30%). The content of thefluoride ion in the obtained bis(fluorosulfonyl)imidetetrapropylammonium salt was 1 ppm. The boiling point of the obtainedsample was 140 to 141° C.

Example 5

Two hundred grams of the final reaction solution prepared as describedin the Example 1 was dissolved in 800 g of water. Then, the solution wasneutralized with 51 g of potassium carbonate, causing the pH of thesolution to increase to 7. The precipitated fluorosulfate potassium saltwas filtered out. When 31 g of 1-butyl-3-methylimidazoliumbromide wasadded to the filtered solution, bis(fluorosulfonyl)imide1-butyl-3-methylimidazoliumbromide salt was separated from the filteredsolution. The separated organic phase was washed with water. Then, bydrying the organic phase, 45 g of bis(fluorosulfonyl)imide1-butyl-3-methylimidazoliumbromide salt was obtained (the recovery basedon the precursor was 32%). The content of the fluoride ion in theobtained bis(fluorosulfonyl)imide 1-butyl-3-methylimidazoliumbromidesalt was 1 ppm.

Comparative Example

The final reaction solution prepared as in the Example 1 was distilledunder reduced pressure to obtain a mixture consisting of fluorosulfateand bis(fluorosulfonyl)imide. Six hundred forty five grams of thismixture was dissolved in 3230 g of methylene chloride. Then, 170 g ofsodium chloride was added to the solution, producingbis(fluorosulfonyl)imide sodium salt. Then, the producedbis(fluorosulfonyl)imide sodium salt was filtered. Methylene chloride inthe filtered solution was distilled away. Then, 326 g ofbis(fluorosulfonyl)imide sodium salt was obtained by further distillingthe residual liquid under ordinary pressure. Thisbis(fluorosulfonyl)imide sodium salt was dissolved in 978 g of water,and neutralized by 154 g of potassium carbonate, causing the pH of thesolution to increase to 7. Then, by distilling away the water in theneutralized solution, 313 g of bis(fluorosulfonyl)imide potassium saltwas obtained. The content of fluoride ion in the specimen was 354 ppm.

While preferred embodiments of the invention have been described above,it should be understood that these are exemplary of the invention andare not to be considered as limiting. Additions, omissions,substitutions, and other modifications can be made without departingfrom the scope of the present invention. Accordingly, the invention isnot to be considered as being limited by the foregoing description, andis only limited by the scope of the appended claims.

INDUSTRIAL APPLICABILITY

The present invention relates to a method for producingbis(fluorosulfonyl)imide salt, a method for producing fluorosulfate, anda method for producing bis(fluorosulfonyl)imide onium salt. In themethod for producing bis(fluorosulfonyl)imide salt, the method forproducing fluorosulfate, and the method for producingbis(fluorosulfonyl)imide onium salt of the present invention, an aqueoussolution is prepared by dissolving a mixed liquid containingbis(fluorosulfonyl)imide and fluorosulfonic acid in water. Then, theaqueous solution is neutralized with an alkaline compound, producingbis(fluorosulfonyl)imide salt and fluorosulfate. By adding an oniumcompound to the neutralized solution and exchanging salts,bis(fluorosulfonyl)imide onium salt can be obtained safely and easily.

The invention claimed is:
 1. A method for producingbis(fluorosulfonyl)imide salt comprising: a step of dissolving, in whicha mixed liquid containing bis(fluorosulfonyl)imide and fluorosulfonicacid is dissolved in water to prepare an aqueous solution; a step ofneutralizing, in which the aqueous solution is neutralized by an alkalicompound to prepare a neutralized solution; and a step of recoveringbis(fluorosulfonyl)imide salt, in which bis(fluorosulfonyl)imide salt isrecovered from the neutralized solution; wherein the total amount of thewater dissolving the mixed liquid in the step of dissolving is 1 to50-fold by mass relative to a mass of the mixed liquid.
 2. A method forproducing bis(fluorosulfonyl)imide salt according to claim 1, wherein,bis(fluorosulfonyl)imide salt is recovered in the step of recoveringbis(fluorosulfonyl)imide salt by extracting the neutralized solutionwith an organic solvent.
 3. A method for producingbis(fluorosulfonyl)imide salt according to claim 1, wherein, the mixedliquid dissolved in water in the step of dissolving is a reaction liquidproduced by a reaction between urea and fluorosulfonic acid.
 4. A methodfor producing bis(fluorosulfonyl)imide salt according to claim 1,wherein, the alkaline compound used in the step of neutralizing is onecompound selected from the group consisting of MOH, M₂CO₃, MHCO₃,ammonia, and amine, wherein M in the chemical formulae, represents oneselected from the group consisting Na, K, Li, and ammonium cation.
 5. Amethod for producing bis(fluorosulfonyl)imide salt according to claim 1,wherein, a content amount of fluorine ion in bis(fluorosulfonyl)imidesalt after the step of recovery is 100 ppm or less.
 6. A method forproducing bis(fluorosulfonyl)imide salt according to claim 1, wherein, acontent amount of fluorine ion in bis(fluorosulfonyl)imide salt afterthe step of recovery is 20 ppm or less.
 7. A method for producingbis(fluorosulfonyl)imide salt according to claim 2, wherein, thealkaline compound used in the step of neutralizing is one compoundselected from the group consisting of MOH, M₂CO₃, MHCO₃, ammonia, andamine, wherein M in the chemical formulae, represents one selected fromthe group consisting Na, K, Li, and ammonium cation.
 8. A method forproducing bis(fluorosulfonyl)imide salt according to claim 2, wherein, acontent amount of fluorine ion in bis(fluorosulfonyl)imide salt afterthe step of recovery is 100 ppm or less.
 9. A method for producingbis(fluorosulfonyl)imide salt according to claim 2, wherein, a contentamount of fluorine ion in bis(fluorosulfonyl)imide salt after the stepof recovery is 20 ppm or less.